Ok, a follow up.... On the 2012 EXC 500 "popping" or backfiring issue that I knew was caused by a lean condition at idle....
I have found by troubleshooting the issue to be 60% caused by the EVAP purge solenoid and EVAP canister system, and the other 40% caused by the SAS valve (secondary air system).
The EVAP purge solenoid system can be disabled by simply unplugging the small two wire connector from the rubber mounted solenoid just under the throttle body (EFI unit) and it will quit allowing outside air into the cylinder. I personally believe that the factory needs to reprogram the ECM/PCM so that the solenoid is NOT energized at idle, but that's my personal opinion, I think they missed the boat in the programming of "when" the EVAP purge solenoid should be open or closed.
HOWEVER, I don't care if they come out with a new program or not because I've learned that it doesn't need to be there anyway, so I've removed the solenoid, the vacuum hoses, the canister (tucked behind the right side of the gas tank) and the little brass fitting that's screwed into the right side of the intake port of the cylinder and replaced the brass fitting with a small metric screw with locktite on the threads. Also to finish up on the removal of the EVAP system you have to re-route the gas tank breather hose to the hole in the frame where it normally goes on the XC-W or other KTM models, or do what I did and purchase the little orange annodized gas cap breather check valve and hose that is way cool looking. (click on the link)
This solves 60% of the popping.
Now for the other 40% of the popping... it's caused by the SAS valve, or secondary air system valve and hose. On the right side of the cylinder you'll see an aluminum valve with about a 1/2" or 5/8" diameter black rubber hose attached and the hose runs up and between the right side of the tank and the frame. This system is also for emmissions and not needed in most states (But KTM had to put it there to sell it in the U.S. as a 50-state legal bike). Remove the hose and the valve from the cylinder and then screw in a 12mm x 1.5mm thread x "as short as you can get it" bolt into the threaded hole in the cylinder with the copper washer and locktite on the threads and you're done! I re-used the aluminum locknut that was on the SAS valve to make my bolt essentially shorter than it actually was so I didn't have to cut my bolt shorter... I spun on the aluminum nut onto my bolt then put on the copper washer, then locktite, then threaded it into the cylinder.
One more thing, when you start the bike after the EVAP removal, it won't idle, you'll have to turn the idle up with the idle knob on the left side of the throttle body. THIS IS BECAUSE the idle screw/knob is actually an air screw and since the idle was adjusted stock with all that extra air being allowed into the cylinder, the idle knob was probably like mine, almost all the way screwed in. In fact, you should be able to kill the engine by turning the idle knob all the way in but in STOCK FORM, you cannot turn the idle down far enough to kill the engine because of all the extra air the other two unnecessary systems are allowing into the cylinder at idle.
I now am finally happy with my 2012 EXC 500.
I also rode it yesterday to 9712 feet in elevation and it idled just fine up there now with the modification, where before the mod it wouldn't idle at that altitude.
Very nice bike,
Scott in Utah